This invention relates to a process for the recovery of valuable materials from slags accumulating in metallothermic processes for the production of metals or ferro alloys, in which a mixture of metal oxides, reducing agents or, additionally, metals is ignited and a metal melt and a slag melt are formed.
Metallothermic processes are metallurgical reactions between certain metal oxides, such as for example molybdenum, tungsten, vanadium, chromium or niobium oxide, with the reducing agents aluminum or silicon, the corresponding metals of the oxides (or even alloys) being formed by spontaneous (exothermic) reaction where additional oxides or metals are present during the reaction. For example, ferromolybdenum, ferrotungsten, ferrovanadium, ferrochromium and also ferroniobium or nickel niobium are produced by this method.
Slags containing varying amounts of the valuable metal oxide (MoO.sub.3, WO.sub.3, Cr.sub.2 O.sub.3, Nb.sub.2 O.sub.5, V.sub.2 O.sub.5) in addition to the oxide of the reducing agent (Al.sub.2 O.sub.3 and/or SiO.sub.2) accumulate in all metallothermic processes. The reason for this lies in incomplete reduction reactions between metal oxide and reducing agent. This case frequently occurs in practice because the reaction cannot quite be completed if a certain content of reduction metal in the end product is not to be exceeded.
The closest prior art in this regard is represented by German Patent Application 3 215 369 which describes one such metallothermic process. This document discloses a measure for increasing the yield of the metal phase which comprises treating the still molten slags from such processes with additional reducing agents in the presence of electrothermal energy until the slag is substantially free from the valuable materials used as metal oxides. The disadvantage of this process lies in the fact that its control is made very complicated by repeated sampling and analysis of the still liquid reactants during the post-reduction phase and in the fact that maintaining the boundary conditions for the content of unwanted reduction metal in the metal phase is determined by very critical process parameters. Accordingly, a compromise has to be established between the purity of the metal phase and the residual content of metal oxides used in the slag.
Accordingly, the problem addressed by the present invention was, and its object is, to provide a process which would not be attended by the above-described disadvantages.